Sexing Wrens Troglodytes troglodytes indigenus using morphological measurements and discriminant analysis

Within the breeding population of a deciduous woodland, male Wrens averaged slightly larger than females in wing length, foot length, head plus bill length and body mass. First-year and older birds were similar for three of these morphometric variables, but the first-year group were shorter-winged than the older birds (by 3%). Despite this, wing length still proved to be a useful discriminator of sex when the data were pooled for all ages (74% of males exceeding the maximum female value of 49.8 mm). A discriminant function utilizing wing length and head plus bill length correctly sexed 96% of individuals in the sample from which it was derived (n = 49 males, 36 females). This function was converted into a predictive equation for the probability of an unknown case being male, and a plot of wing length against head plus bill length along with probability contours which enabled the sexing of unknown cases without the need for calculations. Measurements of the morphological variables investigated were found to be highly repeatable for a single worker, with the exception of body mass which differed substantially between the sexes but which was only moderately repeatable. The methods provided should prove valuable for sexing British mainland Troglodytes troglodytes indigenus, and probably also Western European T. t. troglodytes, but should not be applied to the larger, offshore island races.     

Site tenacity and survival rates of Wrens Troglodytes troglodytes and Treecreepers Certhia familiaris in a Nottinghamshire wood

Mark-recapture data from 20 years of standardized mist-netting were used to investigate site tenacity and adult survival rates of Wrens Troglodytes troglodytes and Treecreepers Certhia familiaris in an English woodland. Within breeding seasons, a high proportion of Wren (but not Treecreeper) recaptures occurred in the same part of the wood as the original capture. Between breeding seasons, a high proportion of recaptures of adult males (but not of adult females) occurred in the same part of the wood as the original capture. Both species experienced exceptionally high mortality during the severe winters of 1978–1979 and 1985–1986, and, in the case of Wren, all or almost all birds which had previously bred in the wood probably died. Outside of these two cold winters, apparent (minimum) adult survival rates of Wrens and Treecreepers showed very different temporal patterns of variation. Wren survival rates were negatively correlated with the number of snow days in winter, whilst Treecreeper survival was negatively correlated with the amount of winter rainfall. After allowing for the influence of winter weather, apparent survival rates of adult Wrens were density dependent, indicating that either mortality or permanent emigration out of the wood was density dependent. There was some evidence from British and Irish ringing recoveries that movements of adult Wrens may be density dependent. The apparent survival rate of adult Wrens was probably an important factor determining the size of the local breeding population.     

The ecology of cooperative breeding behaviour

Ecology is a fundamental driving force for the evolutionary transition from solitary living to breeding cooperatively in groups. However, the fact that both benign and harsh, as well as stable and fluctuating, environments can favour the evolution of cooperative breeding behaviour constitutes a paradox of environmental quality and sociality. Here, we propose a new model – the dual benefits framework – for resolving this paradox. Our framework distinguishes between two categories of grouping benefits – resource defence benefits that derive from group‐defended critical resources and collective action benefits that result from social cooperation among group members – and uses insider–outsider conflict theory to simultaneously consider the interests of current group members (insiders) and potential joiners (outsiders) in determining optimal group size. We argue that the different grouping benefits realised from resource defence and collective action profoundly affect insider–outsider conflict resolution, resulting in predictable differences in the per capita productivity, stable group size, kin structure and stability of the social group. We also suggest that different types of environmental variation (spatial vs. temporal) select for societies that form because of the different grouping benefits, thus helping to resolve the paradox of why cooperative breeding evolves in such different types of environments.     

Effects of nestboxes on the breeding biology of Southern House Wrens Troglodytes aedon bonariae in the southern temperate zone

Nestboxes are known to increase clutch size, enhance breeding success and affect the social mating system of several cavity nesters. Although in recent years various cavity nesters have been studied in nestboxes in South America, the effects of boxes on the biology of the study species are unknown. We evaluated the effects of nestboxes on the breeding biology and social mating system of Southern House Wrens Troglodytes aedon bonariae by comparing birds breeding in nestboxes and tree cavities in two cattle ranches in Buenos Aires Province, Argentina. Southern House Wrens nesting in boxes had higher breeding success but, contrary to studies on the temperate zone, we did not find differences in clutch size between Wrens breeding in nestboxes and tree cavities. The main causes of nest failure in tree cavities were nest predation and flooding of the cavity (70 and 23% of the failures, respectively) while in nestboxes predation and desertion were the most important causes of failure (38 and 34% of the failures, respectively). The social mating system of Southern House Wrens is monogamy with biparental care, and neither was affected by the boxes. Males did not attract secondary females to additional nestboxes; however, nestboxes are safer breeding sites than tree cavities, and females seemed to prefer males with nestboxes on their territory. These results suggest that nest quality alone might be not enough for secondary females to accept polygyny.     

Song sharing and singing strategies in the winter wren Troglodytes troglodytes

The winter wren is a common forest bird living in groups of few adjacent neighbours during the breeding season. Inside each group, males vocally interact in the context of both territorial holding and sexual competition, forming a complex communication network. To study this network, we first analysed song type and syllable repertoires within and between distinct groups. We found a limited number of song types highly stereotyped in length, syntax and syllable composition, frequently shared among neighbours. Between groups, song type and syllable repertoires sharing decreased with increasing distance at a higher rate for song types than for syllables. Then, with continuous recordings, we focused on the dynamics of acoustic interactions between neighbours. We showed that male winter wrens can differentially use their song type repertoire (non-matching strategy), overlap their neighbours and modulate their singing rhythm producing longer inter-song intervals with no change in song length during acoustic interactions.     

Aggressiveness,Boldness and Parental Food Provisioning in Male House Wrens (Troglodytes aedon)

Behavioural syndromes have been identified in a large number of species, yet our understanding of them in an ecological context remains poor. Specifically, there are few data that relate behavioural syndromes to other biologically important behaviours and, ultimately, to reproductive success. In this field study, we examined the aggressiveness and boldness of free‐living male house wrens (Troglodytes aedon) and found a statistically significant positive relationship between these two behaviours (i.e. a behavioural syndrome). When we examined the two axes of this behavioural syndrome in relation to the male's share of provisioning, we found a negative relation between a male's aggressiveness and his provisioning rate, but no relationship between male boldness and provisioning behaviour. These differences in provisioning behaviour among males with different levels of aggression may reflect differences in reproductive strategies or different life‐history trade‐offs among males. Moreover, these results indicate that while some behavioural traits may be correlated, this does not mean that traits that compose the behavioural syndrome cannot evolve independently of one another.     

Conventional and network analyses of song organization and complexity in northern House Wrens (Troglodytes aedon parkmanii)

Among songbirds with large song-type repertoires, there may be functional variation in how individuals organize and display song-type diversity over time. Past studies focusing on conventional measures of song production have been extremely productive. However, network analysis offers a novel set of tools to quantify additional, previously unstudied elements of song organization and display. We studied protracted bouts of singing by 10 male House Wrens (Troglodytes aedon) to (1) test functional hypotheses of variation in song diversity in this species, and (2) evaluate the utility of network metrics in such research. Our analysis included a variety of conventional measures of song production and several standard metrics from network theory to quantify how variably the many song types in a male’s repertoire could be connected to one another and the limitations or diversity of their song sequences. Analysis of conventional variables showed that males produced more and longer songs, at shorter intervals, containing more syllables and more different syllable types, and also more different song types, prior to than after pairing and early in the morning regardless of breeding stage. These results are consistent with the hypothesis that song diversity functions in mate attraction and possibly in territory signaling. In contrast, analyses of network metrics revealed variety in song sequencing by males, but comparatively few and weak effects associated with either breeding stage or time of day. Overall, most song types connected to only a few others and a relatively small proportion of all possible song-type transitions actually occurred. Hence, much of the variety in song sequencing that was possible with the large song repertoires of males was not realized. The latter outcomes, brought to light via network analyses, highlight an important paradox for future research on this and related species with large song repertoires.     

House Wrens Troglodytes aedon reduce repertoire size and change song element frequencies in response to anthropogenic noise

Anthropogenic noise (≤ 3 kHz) can affect key features of birds’ acoustic communication via two different processes: (1) song‐learning, because songbirds need to hear themselves and other birds to crystallize their song, and (2) avoidance of song elements that overlap with anthropogenic noise. In this study we tested whether anthropogenic noise reduces the number of song elements in the repertoire of House Wren Troglodytes aedon, an urban species. Additionally, we tested whether the proportion of high‐frequency elements (i.e. elements where the minimum frequency is above 3 kHz) is related to anthropogenic noise levels, and how the frequencies and duration of shared elements between males change with different levels of anthropogenic noise. We recorded 29 House Wren males exposed to different anthropogenic noise levels (36.50–79.50 dB) during two consecutive breeding seasons from four locations. We recorded each male on 2 days during each season continuously for 50 min (we collected 104 h of recordings) and measured anthropogenic noise levels every 10 min inside each male territory during the recording period. In general, individuals inhabiting noisier territories had smaller repertoires. However, only in two locations with anthropogenic noise levels between 38.60 and 79.50 dB did males inhabiting noisier territories have smaller repertoires. In the other two locations with lower anthropogenic noise (36.50–66.50 dB), the anthropogenic noise inside each territory was not related to the repertoire size. Individuals inhabiting the noisiest location showed a tendency to include more high‐frequency elements in their songs. In 26% of the elements, the anthropogenic noise affected their frequency features. Our results showed that not all House Wrens inhabiting urban environments modify their songs at the highest level of organization (i.e. repertoire) to reduce the masking effect of anthropogenic noise on acoustic communication.     

Song Degradation during Propagation: Importance of Song Post for the Wren Troglodytes troglodytes

The degradation of bird sounds during long-range propagation depends on different parameters such as density of vegetation, height from the ground and atmospheric perturbations. We investigated whether the wren Troglodytes troglodytes, a bird species which has a high-pitched song that is very susceptible to degradation and lives in an environment that is very restricting for sound propagation, has any advantage in choosing relatively high song posts. Song degradation was investigated by analysing sound attenuation, duration of notes and silences, spectrum composition, modifications of frequency-modulated notes and amplitude fluctuations. Our data show that the choice of an elevated song post improves the reliability of all song parameters and increases the propagation distance of the song. It also improves the male wren's ability to hear opponent songs. The results are discussed from an ecological point of view.     

Molecular ecology of social behaviour: analyses of breeding systems and genetic structure

Molecular genetic studies of group kin composition and local genetic structure in social organisms are becoming increasingly common. A conceptual and mathematical framework that links attributes of the breeding system to group composition and genetic structure is presented here, and recent empirical studies are reviewed in the context of this framework. Breeding system properties, including the number of breeders in a social group, their genetic relatedness, and skew in their parentage, determine group composition and the distribution of genetic variation within and between social units. This group genetic structure in turn influences the opportunities for conflict and cooperation to evolve within groups and for selection to occur among groups or clusters of groups. Thus, molecular studies of social groups provide the starting point for analyses of the selective forces involved in social evolution, as well as for analyses of other fundamental evolutionary problems related to sex allocation, reproductive skew, life history evolution, and the nature of selection in hierarchically structured populations. The framework presented here provides a standard system for interpreting and integrating genetic and natural history data from social organisms for application to a broad range of evolutionary questions.     

Spatial and temporal variation in breeding parameters of two south-temperate populations of House Wrens

Studies of variation in breeding parameters are often based on temporal analyses of a single population. However, to differentiate between the effects of regional and local factors, neighboring populations with limited interpopulational dispersal need to be compared. We studied two nearby (< 5 km apart) populations of House Wrens (Troglodytes aedon bonariae) at two ranches (Los Zorzales, 10 years; La Esperanza, 13 years) in south-temperate Argentina to assess the possible effects of regional and local factors on breeding phenology. For each breeding season, we recorded laying dates, clutch sizes, and length of the breeding season, and estimated the reproductive synchrony of first and second breeding attempts. We examined how these breeding parameters were affected by weather, population density, and rates of nest failure. With favorable temperatures during the pre-reproductive period (September–October), wrens in both populations initiated first breeding attempts earlier. However, ordinal laying dates were also affected by local factors, with wrens at Los Zorzales initiating breeding attempts earlier than those at La Esperanza. We found a spatial correlation in clutch sizes between populations for the 2007–2012 breeding seasons, but clutch sizes of first and second nesting attempts showed low variability. Reproductive synchrony of first nesting attempts varied among years, suggesting an effect of regional factors. However, we detected no synchronization between populations and were unable to identify environmental variables that explained the temporal variation. Ordinal laying dates of second clutches were strongly correlated with the ordinal laying dates of first clutches. We also found that the length of breeding seasons was longer when daily nest mortality rates were lower. Although environmental factors seemed to affect the decision of when to start breeding, pairs with successful first nesting attempts were more likely to initiate second nests, thus affecting the length of the breeding season. The spatial variation and temporal variation of the breeding parameters of House Wrens in our study provide evidence of marked plasticity in their breeding decisions and allowed us to identify local and regional environmental factors related to this variation.     

Genetic divergence of Troglodytes troglodytes islandicus from other subspecies of Eurasian wren in northwestern Europe

The Icelandic subspecies of Eurasian wren Troglodytes troglodytes islandicus has been described as a large wren which is sedentary on the island. It is one member of a large passerine complex which is widely distributed over the Holarctic except the Arctic. The taxonomic affiliation of the subspecies is mainly based on variation in plumage and on the song complexity. This study investigated the genetic differentiation of T. t. islandicus among the Eurasian wren subspecies in northwestern Europe, and especially in relation to its geographically proximate populations in the Faroe Islands, Scotland, southern Norway, Sweden and Denmark. Troglodytes t. islandicus and the Faroese subspecies (T. t. borealis) were genetically differentiated from the other subspecies (T. t. indigenus and T. t. troglodytes) with an estimated time of divergence from this group during the last glacial maximum; 21 thousand years before present (KYBP) [44–8]. A clear but a more recent split was observed between T. t. islandicus and T. t. borealis 12 KYBP [28–4].     

The cichlid fishes of Guyana, South America, with notes on their ecology and breeding behaviour

Field studies in Guyana, north-eastern South America, from 1957 to 1962 included observations on the ecology and behaviour of cichlids in natural waters. Collections made were examined at the British Museum (Natural History) together with other cichlid material from Guyana. This paper records these observations and gives keys for the field indentification of these cichlids. Fifteen genera comprising at least 35 species occur in Guyana, mostly species with a wide distribution in tropical South America. In the predatory Cichla ocellaris which grows larger than other South American cichlids, growth continues long after the fish matures. Males tend to be larger than associated females. The behaviour of Cichla ocellaris and Cichlasoma festivum when guarding their young suggests that the caudal ocellus has a vital role in the orientation of young to parent. Most of these cichlids in which breeding habits are known are substratum-spawners. An attachment gland, producing viscous threads, was found on the heads of recently hatched Geophagus jurupari young, although this species carries the young in the mouth.     

The evolutionary ecology of decorating behaviour

Many animals decorate themselves through the accumulation of environmental material on their exterior. Decoration has been studied across a range of different taxa, but there are substantial limits to current understanding. Decoration in non-humans appears to function predominantly in defence against predators and parasites, although an adaptive function is often assumed rather than comprehensively demonstrated. It seems predominantly an aquatic phenomenon—presumably because buoyancy helps reduce energetic costs associated with carrying the decorative material. In terrestrial examples, decorating is relatively common in the larval stages of insects. Insects are small and thus able to generate the power to carry a greater mass of material relative to their own body weight. In adult forms, the need to be lightweight for flight probably rules out decoration. We emphasize that both benefits and costs to decoration are rarely quantified, and that costs should include those associated with collecting as well as carrying the material.     

Reaction to conspecific degraded song by the wren Troglodytes troglodytes: Territorial response and choice of song post

We investigated the response of the wren Troglodytes troglodytes to playback of a territorial song degraded by long-range propagation. It appears that the wren is sensitive to this degradation since the territorial reaction is less intense with the degraded song than with the undegraded one. However, the degraded song is still considered by the receiver as a specific territorial aggressive signal. This differential response suggests that the male wren can use the degradation characteristics of the signal to adapt its territorial reaction. Indeed, in response to this stimulus, the receiver wren chooses a higher song post. By so doing, the bird improves both the propagation distance of the emitted song and the receiver's ability to hear the opponent's song. This behavioural change may correspond to a communication strategy, counteracting the environmental constraints on sound propagation. Therefore, in response to sound degradation during long-range propagation, birds may have developed behavioural adaptations complementary to the various adaptations concerning song structure and coding-decoding processes.     

The breeding behaviour of Gammarus duebeni

The breeding behaviour of a population of Gammarus duebeni is investigated. The breeding system includes a precopulatory guarding phase by a male of a female and the length of this phase varies markedly over the season. Large size is not of as great advantage in reproductive competition between males as in a stream population of G. pulex. In the spring of 1981 oligochete worms, Nais elinguis, were found in the brood pouches of some females; eggs were seldom present with the worms but rather amorphous debris. The occurrence of the worms and the debris in the females' pouches coincided with the pattern of abundance of the worms previously reported.     

Predatory behaviour ofScatophaga stercoraria under laboratory conditions

Laboratory experiments tested the effectiveness ofScatophaga stercoraria (L.) as a predator of various insect species. Photophases, ages and gender of predators and effects of dung presence on predation rates were compared for either sex using counts of prey cadavers, behavioral observations and oviposition rates. Males consistently killed more prey than females, but longer photophases did not significantly increase daily predation rates. Nine to 10-day-old flies approaching sexual maturity achieved highest predation rates. Dung was found to affect predatory behaviour but not cumulative predation. Predatory behaviour of sexually mature males was more affected than female behaviour by the presence of dung, whereas sexually immatures flies showed no response to dung presence. Preconditioning ofS. stercoraria adults using 3 prey species of different sizes did not affect the prey chosen in subsequent random choice experiments. Larger prey species such asMusca domestica (L.) orDelia antiqua (Meigen) were preferred toDrosophila sp. by both sexes ofS. stercoraria. This species may be a useful predator for future integrated pest management techniques in vegetable crops or control of house flies in barns.